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Chapter 8. Regular Expressions

The limits of my language mean the limits of my world.

Ludwig Wittgenstein

The world’s first computers were women. They were the employees of research centers and national labs, where they inspected data, executed
algorithms, and reorganized data. Their job title was “computer”
because they computed. In the early days, computing meant evaluating
raw data by hand for a variety of applications and experiments,
including, famously, the Manhattan Project.

You, too, may have raw data. However, today’s data should not be processed by
hand. Today’s data is usually too big, the risk of carpal tunnel is
too high, and computers are too powerful to justify that. Processing
raw textual physics data may require:

Searching for and correcting irregularities

Finding and replacing text across hundreds of files

Evaluating mathematical expressions

Manipulating number formatting

Rearranging column-formatted data

This chapter will discuss regular expressions, a common syntax for matching
patterns of characters in text files, data files, filenames, and other sequences
of characters. This syntax is ubiquitous in the programming world because it
can turn an enormous, tedious file cleanup task into a tiny one-line command.
Additionally, it can help with day-to-day command-line navigation, file
parsing, and text editing.

In the shell, regular expressions can be used to clean up and analyze raw data in conjunction with the search and print programs that will ...

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